This application is based upon and claims priority of Japanese Patent Application No.2002-077714, filed in Mar. 20, 2002, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, a semiconductor device having a capacitor and a method of manufacturing the same.
2. Description of the Prior Art
In recent years, as one of the semiconductor memories in which the information can be held after the power supply is shut off and into/from which the information can be written/read with saving the electric power, the FeRAM (Ferroelectric Random Access Memory) is watched with interest.
The FeRAM has the structure that can store the information by utilizing the hysteresis characteristic of the ferroelectric substance. As the ferroelectric material, lead zirconate titanate (PZT), etc. are employed.
In the FeRAM, the first capacitors formed in the memory cell region A and the second capacitor formed in the peripheral circuit region to increase or decrease the power supply voltage are present.
The first capacitors have the function of storing the information based on the polarization inversion (hysteresis) as the feature of the ferroelectric material. The ferroelectric material that is excellent in the ferroelectric characteristics such as the saturation characteristic, the fatigue characteristic, etc. is required.
The fatigue characteristic indicates the feature of deterioration of the memory when the number of writing operations is increased. Also, the fatigue characteristic is the index indicating whether or not the memory can exhibit its sufficient capability at the low voltage.
The second capacitor does not particularly need the employment of the ferroelectric material. The material that has the large capacitance and the small leakage must be selected, like the capacitor employed in the DRAM, etc.
However, in the FeRAM, the dielectric film in both the first capacitor and the second capacitor is constructed by the ferroelectric material.
The reason why the ferroelectric material is selected as the dielectric film of the second capacitor resides in that the capacitance per unit area can be increased rather than the case where the dielectric film is constructed by the silicon oxide, like the capacitor of the DRAM. The ferroelectric material has the large dielectric constant rather than the silicon oxide. For example, the dielectric constant of the silicon oxide is 3.4 whereas the dielectric constant of the PZT as the ferroelectric material is in excess of 100.
In the FeRAM steps in the prior art, the first capacitor and the second capacitor are formed by the same steps, and the area of the second capacitor is formed larger than that of the first capacitor.
However, it is advantageous from the viewpoints of the magnitude of the capacitance, the magnitude of the dielectric constant, as described above, to construct the dielectric film of the capacitor formed in the peripheral circuit region with the ferroelectric material, but such structure has the drawback that the leakage current characteristic is wrong. In other words, such a disadvantage is caused that, as the characteristics of the first capacitor are improved more highly, the leakage current of the second capacitor is increased much more.
It is an object of the present invention to provide a semiconductor device capable of giving characteristics, which are fitted for applications, to plural types of capacitors formed on the same substrate respectively, and a method of manufacturing the same.
The above object of the present invention is overcome by providing a semiconductor device which comprises an insulating film formed over a semiconductor substrate; a first capacitor having a first lower electrode, a first ferroelectric film, and a first upper electrode, which are formed sequentially over the insulating film in a first region; and a second capacitor having a second lower electrode, a second ferroelectric film, and a second upper electrode, which are formed sequentially over the insulating film in a second region; wherein the first ferroelectric film is formed of first ferroelectric material that comprises plural of elements containing a first element, the second ferroelectric film is formed of second ferroelectric material that comprises plural of elements containing the first element, and a concentration of the first element in the second ferroelectric film is lower than a concentration of the first element in the first ferroelectric film.
Also, the above object of the present invention is overcome by providing a manufacturing method of a semiconductor device which comprises the steps of forming an insulating film over a semiconductor substrate; forming a first conductive film over a first region and a second region of the insulating film; forming a ferroelectric film, which comprises plural of elements containing a first element, on the first conductive film; forming a second conductive film on the ferroelectric film; patterning the second conductive film to form a first upper electrode constituting first capacitor in the first region and also form a second upper electrode constituting a second capacitor in the second region; patterning the ferroelectric film to form a first dielectric film constituting the first capacitor in the first region and also form a second dielectric film constituting the second capacitor in the second region; patterning the first conductive film to form a first lower electrode constituting the first capacitor in the first region and also form a second lower electrode constituting the second capacitor in the second region; and reducing selectively a concentration of the first element in the ferroelectric film of the second dielectric film lower than a concentration of the first element in the ferroelectric film of the first dielectric film.
According to the present invention, the dielectric films of the first capacitors and the dielectric film of the second capacitor, which have the different applications, are formed of the ferroelectric material that contains plural elements respectively. Then, a concentration of a predetermined element, which serves as a leakage-current increasing factor, for example, in the ferroelectric material is reduced selectively low in the dielectric film of the second capacitor. Adjustment of the concentration of the predetermined element can be executed by the annealing after the ferroelectric film is formed.
Therefore, plural types of capacitors can be formed by forming the ferroelectric film only one time in response to the applications. Thus, steps of forming the semiconductor device are never largely increased in order to form individually the capacitors in response to the applications, and also the increase in cost can be suppressed.
For example, the PZT film is employed as the ferroelectric film, the leakage current of the second capacitor can be reduced by reducing the concentration of the lead as the constitutive element by virtue of the annealing. Also, if the first capacitors are covered with the protection insulating film in order to prevent the elimination of the constitutive element, the deterioration of the saturation characteristic and the fatigue characteristic of the first capacitor by the annealing is avoided.